Container for asphalt



Patented Sept, 24, 1935 ,rwt

No Drawing.

Application April 3, 1933, Serial N0. 664,200. In Great Britain April 13, 1932 i 7 Claims. ((11. 91-68) This invention concerns metal containers such as barrels, drums or the like for holding asphalt, under which expression are for the purpose of this invention included all those solid, semi-solid or plastic bituminous substances, such as bitumen, tar or pitch, whether derived from naturally occurring depositsor obtained artificially by the distillation, evaporationor concentration of crude petroleum, coal tar or the like materials, or from derivatives thereof, which by virtue of their chemical or physical properties have a tendency to adhere to the surfaces of metals.

This adhesion of asphalt to thesurface of a metal is due to the fact that asphalt, whether in a molten condition or after it has solidified at ordinary temperatures, has a low surface tension as compared with that of metals, and the conditions of adherence are determinedby the tendency at the asphalt metal interface for the surface energy at'that interface to reach a minimum value. v

When required for use, the asphalt is separated by stripping, by means of a physical operation and without the application of heat, from the little mechanical strength and have little adherence to the metal, and if cracked,'broken or displaced during the handling or transport of the container, such imperfections in the coatings enable the asphalt to penetrate through to the metal and adhere thereto. Again, the coatings remain for the most part attached to the sur faces of the detached asphalt and thereby spoil its appearance, and being foreign toits nature may impair its subsequent utilization in the industry.

The present invention. has for its object to avoid such disadvantages and provides an improved method of treating the interior surfaces of such metal containers, or the surfaces of any substances other than asphalt-which may already exist upon such metal surfaces, previous to the introduction of the asphalt into the container, whereby the natural tendency of the asphalt to adhere to such surfaces is considerably lessened or removed, and the subsequent separation of the one from the other by the application of mechanical force is greatly facilitated.

According to the invention, the improved method of treating the interior surfaces of the metal containers destined to contain asphalts, in

order to render such non-adherent to,

or easily separable by physical force from the asphalts, consists in applying to the interior surfaces of the containers, liquid or semi-liquid films or coatings so selected that their work of adhesion for the interior surfaces of the containers 5 is greater than the work of cohesion of the films or coatings for themselves, while the work of adhesion of the applied films or coatings for the surfaces of the asphalts is less than the work of cohesion of the films or coatings for them- 10 selves in order that the films or coatings will more readily wet, adhere to and combine with such container surfaces than wet, adhere to and combine with the surfaces of the asphalts. The

films or coatings may be regarded as acting selectively, being attracted towards the container surfaces, but substantially repellent towards'the asphaltsurfac'es. Such applied films or coatings thus act in place of or substitute the natural surfaces of the metal containers or the artificial surfaces of any other materials such as artificial oxides or a coating of clay, lime, zinc, paint or pigment which may have been applied thereto. The applied films, or coatings may consist of aqueous solutions of water-soluble salts in concontrations such that the surface tensions of the aqueous solutions are higher than the surface tensions of the asphalts and lower than the surface tensions of the interior surfaces of the containers, or the applied films or coatings may consist of aqueous solutions of bases and acids capable of interacting chemically to formwater-soluble salts in concentrations such that the surface tensions of the solutions of the salts are higher than the surface tensions of the asphalts and lower than the surface tensions of the interior surfacesv of the containers. Thus the applied films or coatings may consist of aqueous solutions of the chlorides or nitrates of the alkali metals including ammonium or the alkaline earth metals or of 40 iron, aluminium, zinc, manganese or magnesium. Again the applied films or coatings may consist of aqueous solutions of the sulphates, bisulphates, thiosulphates, sulphites, bisulphites, orthophosphates, metaphosphates or pyrophosphates of the alkali metals including ammonium or the sulphates of iron, aluminium, zinc, manganese or -magnesium. 'Furthermore the'applied films or coatings may contain the carbonates or bicarbonates or sulphides of the alkali metals includ- 0 ing ammonium or of iron, aluminium, zinc, manganese or magnesium in admixture with aqueous solutions of free acids or aqueous solutions of acid salts in such proportions that the components by chemical reaction produce the corre 5 sponding salts of the metals in the solutions in suchconcentrations that they more readily wet, adhere to and combine with the surfacesof the containers than wet, adhere to and combine with the asphalts while generating carbon dioxide and may become visible rust, while if the joints of the hydrogen sulphide respectively. As another alternative the applied films or coatings may consist of aqueous solutions of acids, such as sulphuric acid, hydrochloric acid, nitric acid, or phosphoric acid in such concentrationsthat they react with the metal surfaces of the containers to form in solution the corresponding sulphate, chloride, nitrate or phosphate of the metals while generating bubbles of gas. As a further alternative the applied films or coatings may consist of aqueous solutions of acids such as sulphuric acid, hydrochloric acid, nitric acid or phosphoric acid admixed with finely divided metals such as iron or zinc or in the case of hydrochloric acid finely divided aluminium in such proportions that they react to form the sulphates, chlorides, nitrates or phosphates ofthe metals while generating bubbles of hydrogen. If desired the applied films or coatings may consist of aqueous solutions of alkalies such as sodium or potassium hydroxides admixed with finely divided metallic aluminium in such proportions that they react to form the aluminates of the alkali metals while generating bubbles of hydrogen. Again the applied films or coatings may consist of potassium soap solutions or of aqueous solutions of the alkaline salts of the fatty acids admixed with polyhydric alcohols such as glycerol. If desired the applied films or coatings may consist of or contain solutions of substances such as sodium bicarbonate or ammonium carbonate capable of liberating bubbles of gas on the application of heat or they may, consist of liquids containing dissolved or occluded gases such as air, carbon dioxide or hydrogen. In 'these last two examples the liberation of the gases facilitates the separation of the asphalts from the surfaces of the containers. The solutions of the applied films or coatings should be of such concentrations that they more readily wet, adhere to and combine with the surfaces of the containers than wet, adhere to and combine with theasphalts. 1

When the-containers are of iron or steel which has been given the form of a cylindrical drum by a rolling operation, and the tops, bottoms and lids are formed by a stamping operation, it is usually the case that the coating of oxide or mill scale" originally possessed by the steel sheets becomes partially or wholly removed or destroyed .by the aforesaid mechanical operations of rolling or stamping. The metal thus exposed by the removal of the mill scale quickly acquires a fresh coating of oxide by exposure to the atmosphere, which coating may be a mere film invisible to the unaided eye, or by longer exposure to the air container have been made by welding, the heat employed in the latter operation may considerably accelerate the formation of and final thickness of the coating of oxide.

, In practice, therefore, it occurs that the sur-- face which by the present invention has to be treated in order to prevent its adherence to asphalt, may not always be uniform' or have the same surface tension in all its parts, and in order therefore to carry out successfully the object of the invention the film or coating must be so chosen and constituted as-to suit the nature of the interior surface concerned.

Again the various forms of asphalt destined to becontained in thesteel oriron drumsmayvary considerably as regards their physical and chemical properties and it isnecessary therefore to select a film or coating suitable to the asphalt surface involved. This is the more a bewet or adhere to asphalt.

cause the asphalt first comes in contact with the interior surface of its container when in a molten state and gradually cools when in contact with the said surface. Not only does the surface tension of the asphalt change when passing from 5 the molten to the final semi-solid or solid state which it assumes within its container, but it is known to be liable to contain substances in suspension or solution which vary according to its origin or method of manufacture, and these adventitious substances may concentrate at-the surface or at the interface between its surface and 4 the applied film and thereby change the interfacial tension between the two.

Since both the interior surfaces of the container and the asphalt it is destined to contain are liable to vary, preliminary experiments may have to be carried out in order to select suitable films or coatings, and these experiments may be assisted by measuring the surface tensions and interfacial tensions involved by any known means.

The following examples serve to illustrate how the invention is carried into effect.

In the examples the asphalt employed was a soft and adhesive variety having the qualities specified below in accordance with the terms of definition known and accepted in the industry:

Specific gravity 25/29 c 1.oo to 1.04 Penetration at 25 (2--.. l80 to 200 Ductility above 100 cms.

Melting point (Ring and Ball) about 40 C. Surface tension in air at 25 C about 30 dynes/cms.

of the containers.

1. The interior surface chosen was clean and smooth, free from oil, grease or rust, and had only the natural coating of mill scale, or the 60 acquired coating .of oxide produced by the heat of welding.

The film consisted of a solution of water-soluble salt or salts, preferably having a surface tension in air at 20 C. of from 70 to 95 dynes/cm. As suitable salts may be mentioned ordinary commercial varieties of the chlorides of the alkali metals including ammonium, or of the alkali earth metals, or of aluminium, iron, manganese, zinc or magnesium. It was found that the chlorides of the above mentioned metals. or cations could be substituted by the corresponding nitrates, or by thekulphates, bisulphates, thiosulphates, sulphites, bisulphites, orthophosphates, metaphosphates, pyrophosphates, of the alkali metals including ammonium or the sulphates of iron, aluminium, zinc, manganese or magnesium in concentrations such that they more readily wet and adhere to steel or iron oxides than they A solution of calcium nitrate in water, the solution having a density of 1.145 at 60 F., prp-- vides a suitable film or coating, which may be applied to the interior surface of the drum by P ting or spraying at the rate of about cc.

while it is still moist, the asphalt may be poured therein. at the usual filling temperature, which should be insuilicient to evaporate the moisture.

The lid may then be treated with the same solution and fixed in position.

2. The interior surface of the container was contaminated with oil or grease and the solutions mentioned in Example 1 could not be used with success because the oil or grease prevented the aqueous solutions from wetting or adhering to the Surface. The container was therefore heated to remove the oil or grease, whereupon one or other of the solutions in Example 1 was applied to the surfaces and the asphalt filled in as before. Alternatively the container was washed with a solvent for oil or grease.

In another case when slight contamination of the surface by oil or grease was present the -applied film-forming material consisted of a solution of soap, so chosen as regards its nature and concentration that it more readily wetted or adhered to the slightly oily surface of the container than it did to the surface of the asphalt.

It has been found that the ordinary commercial variety of potassium soap known as soft. 'sop" is'specially useful for this purpose, a suitable solution containing from 8 to 15% by weight dissolved in distilled water. Advantageously the solution may have m xed with it small quantities of glycerine or similar hygroscopic material. Solutions of other water-soluble soaps may also be employed with or without the addition of suitable materials such as the silicates of sodium or potassium, hydrate of ammonium or polyhydr'c alcohols such as glycerol, which decre se their wetting powers and tendency to adhere to asphalt, and increase their wetting=power and tendency to adhere to the interior surfaces of the containers.

3. The interior surface of the container was very rusty or contained particles of oxide, mill scale or other surface projections. which would penetrate the very thin applied film and eventually reach the asphalt surface so as to cause it partially to adhere. In this case the film applied was a liquid containing in suspension a filler which rendered the surface smooth and Grams Black oxide of iron in fine powder 15 Soft soap 10 Glycerine 2 Water to which, if necessary, a suspending agent may be added.

If the container has already been coated with clay, lime and the like, the coating may be removed by washing or other suitable means, and the container then treated according to the present invention.

According to"the invention the non-adherence to asphaltmay be further secured by incorporating in the applied films a. substance or substances capable of generating bubbles of gas at the asphalt (film interface or metal) film interface. Thus the liquid may consist of an aqueous solution of 5 sulphuric acid, hydrochloric acid, nitric acid or phosphoric acid which will react with the metal of the containers to form in solution the corresponding sulphate, chloride, nitrate or phosphate, while generating bubbles of gas. Again the liquid 1 may contain sodium carbonate or sodium bicarbonate, or ferrous sulphide or again finely divided iron, zinc, or aluminium, together with sulphuric acid, hydrochloric acid, nitric acid or phosphoric acid in such concentrations that they 15 react to form the corresponding sulphate, chloride, nitrate or phosphate of the metals, while generating carbon dioxide, hydrogen sulphide or hydrogen or again the liquid may consist of aqueous solutions of alkalies such as sodium hydroxide, admixed with finely divided aluminium where sodium aluminate in solution is formed and bubbles of hydrogen are given off.

vThe applied film while being adherent to the surface of the container may also have its tendency to wet, adhere to or combine with the asphalt surface, diminished or removed by having incorporated a substance or substances capable of generating bubbles of gas through the agency of moderate heat, such as that supplied by the molten asphalt itself when it comes in contact with the applied film. Alternatively, the applied film may have a gas such as air or carbon dioxide dissolved or occluded in it, in such a manner that such gas will tend to collect in the form of bubbles at the 35 asphat (film interface or metal) film interface.

The above examples are sufiicient to explain the manner in which the'invention may be carried out with a soft variety of asphalt, and with containers varying as regards the nature and condition of their interior surfaces. With other varieties of asphalt and other conditions, the invention may be modified so as to suit the inevitable variations of the surfaces involved, so long as the applied films or coatings conform to the general principles set forth as essentially a part of the invention, namely that the applied'films or coatings shall be so selected that their work of adhesion for the interior surfaces of the containers is greater than the work of cohesion of the films or coatings for themselves, while the work of adhesion of the applied films or coatings for the surfaces of the asphalts shall be less than the work of cohesion of the films for themselves in order that the films or coatings will more readily wet, 55 adhere to and combine with the surfaces of the containers.

What I claim is:

1. A method of treating the interior surfaces of metal containers destined to contain asphalt, 60 which consists in applying to the interior surfaces of a metal container a liquid film consisting of aqueous solutions of a salt of the group consisting of the alkali-metals including ammonium, the alkaline earth'metals and iron, aluminum, zinc, 65 manganese and magnesium, said film having an adhesion tension for the interior surfaces of said metal container greater than the cohesion tension of the film for itself and having an adhesion tension for the surfaces of asphalt less than the 00- 70 hesion tension of the film for itself.

. 2. A method of treating the interior surfaces of metal containers destined to contain asphalt, which consists in applying to the interior surfaces of a metal container a liquid film consisting of an 7 aqueous solution of a chloride of the group consisting of the alkali-metals including ammonium, the alkaline earth metals and iron, aluminum, zinc, manganese and magnesium, said film having an adhesiontension for the interior surfaces of said metal container greater than the cohesion tension of the film for itself and having an adhesion tension for the surfaces of asphalt less than the cohesion tension of the film for itself.

3. A method of treating the interior surfaces of metal containers destined to contain asphalt, which consists in applying to the interiorsurfaces of a metal container a liquid film consisting of an aqueous solution of a sulphate, bisulphate, thiosulphate, sulphite, bisulphite, orthophosphate, metaphosphate or pyrophosphate of the group consisting of the alkali-metals including ammonium, the alkaline earth metals and iron, aluzinc, manganese and magnesium, said film having an adhesion tension for the interior surfaces of said metal container greater than the cohesion tension of the film for itself and having an adhesion tension for the surfaces of asphalt less than the cohesion tension of the film for itself.

4. A method of treating the interior surfaces of metal containers destined to contain asphalt, which consists in applying to the interior surfaces of a metal container a liquid film consisting of an aqueous solution of a sulphate of the group consisting of the alkali metals including ammonium,

. the alkali-earth metals and iron, aluminum, zinc,

manganese and magnesium, said film having an adhesion tension'for the interior surfaces of said metal container greater than the cohesion tension of the 151mm itself and having in adhesion tension for the surfaces of asphalt less than the cohesion tension of the film for itself.

'5. A method of treating the interior surfaces of metal containers destined to contain asphalt, which consists in applying to the interior surfaces of a metal container an aqueous solution of an acid of such concentration that it will react with the metal surfaces of the container to form an 5 aqueous film of the corresponding salt of the metal, said film having an adhesion tension for the interior surfaces of said metal container greater than the cohesion tension of the film for itself and having an adhesion tension for the surfaces of asphalt less than the cohesion tension of the film for. itself.

6. A method of treating the interior surfaces of metal containers destined to contain asphalt, which consists in applying to the interior surfaces of a metal container an aqueous solution of hydrochloric acid admixed with finely divided aluminum in such proportions that an aqueous film of aluminum chloride is formed, said film having an adhesion tension for the interior surfaces of said metal container greater than the cohesion tension 'of the film for itself and having an adhesion tension for the surfaces of asphaltless than the cohesion tension of the film for itself. 1

7. A method of treating the interior surfaces of metal containers destined to contain asphalt which consists in applying to the interior surfaces of a metal container an aqueous solution of an acid admixed with finely divided metal in such proportions that they react to form an aqueous film of the corresponding salt of the metal, said film having an adhesion tension for the interior surfaces of said metal container greater than the cohesion tension of the film for itself andhaving an adhesion tension for the surfaces of asphalt less than the cohesion tension of the film for itself.

JAMES MCCONNELL SANDERS. 

